I don't know those models enough to provide an answer, but test again with stabilisation off - sometimes on a tripod, it 'fights' & comes out worse than with it off.
– TetsujinFeb 10 at 17:30

Was the flash on or off camera? What specific flash model? What Tv with flash? What Tv without flash? Av and ISO for each shot? What exposure mode was used for the flash and non-flash shots?
– Michael CFeb 10 at 17:36

Flash was off camera using a wireless link - Yongnuo 600 ex RTII unfortunatly I don't have all the other settings
– Duncan_wFeb 10 at 17:42

2

Can we have the whole EXIF data (add to your question)? @Tetsujin: I have hard time coming up with a scenario where the IS produces two sharp images and not a blurred one (exposure) and a sharp on (flash).
– xenoidFeb 10 at 17:54

1

Just my 2 cents: I already came to the problem that using IS/OS/VR/OIS on tripod causing ghosting. also the manufacturer recoment to turn it of when using a tripod.
– HoritsuFeb 11 at 10:24

4 Answers
4

Looks like it's related to image stabilization as Tetsujin suggested. Managed to replicate the issue. Switched off the IS and the Ghosting went away. It is a new IS lens (Latest Sigma 105mm macro IS). Guess I just need to remember to switch it off in these circumstances.

If you feel your answer answers your question, you can mark it as the answer.
– xiotaFeb 12 at 8:50

The Sigma 105mm macro does this. I'm not sure if it's at the start or the end of the exposure, but releasing the shutter triggers the IS to sort of 'reset' (I guess to maximize its range during exposure) If you're looking through the viewfinder you can see the image physically shift as you take the shot. I've never tested, and you didn't say what flash settings you were using, but if it was front or rear curtain sync you should be able to figure out if this is affecting the start or end of the exposure. I would expect one of front/rear curtain sync to produce a better image than the other.
– J...Feb 12 at 19:42

In any case, turn it off on the tripod - especially with flash. You just don't need it. Save your batteries.
– J...Feb 12 at 19:44

As I understand it, the problem is as follows. Stabilization works by having some lens elements move around to correct for the the movement of the whole assembly. As Isaac Newton teaches us, every action has an equal and opposite reaction so, when the stabilizer moves lens elements to the left, that nudges the whole lens slightly to the right. If you're shooting hand-held, this isn't a problem, because that little nudge is dwarfed by your hands shaking around. However, when the lens is mounted on a tripod, that nudge is the biggest movement the lens feels. So it tries to correct for it by moving the stabilization elements in the opposite direction. That creates another nudge which the lens also tries to correct. So you end up in a feedback loop where the lens is shifting itself around the whole time, giving a blurry image.

Some newer stabilization systems switch themselves off if they detect that there's so little movement that the lens is likely on a tripod. Other systems, such as the one on your lens, require the user to switch off stabilization when a tripod is being used.

Almost all lenses with IS made since about the year 2000 have auto-sensing modes to prevent feedback loops when used on a tripod. Only a handful of early stabilized lenses actually demonstrated this phenomenon. But once an idea about a "new" technology gets out there, it's hard to ever change the perception, even though most later examples do not demonstrated the issue.
– Michael CFeb 12 at 4:44

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@MichaelC Well, I quoted and linked to Sigma's manual for this lens. That manual clearly states that stabilization shouldn't be used on a tripod. The OP also found that switching off stabilization fixed the problem. Are you saying that there's some other reason for this?
– David RicherbyFeb 12 at 10:41

It is definitely caused by the flash (shot of the exact same scene without flash removed the ghost image).

Not necessarily. The difference could have been something else only tangentially related to using the flash. When comparing the shot taken with the flash and the shot taken without flash:

What exposure mode were you using in each shot?

Did any of the exposure parameters (ISO, Tv, Av) change?

Was the camera set to a specific ISO setting or was 'Auto ISO' enabled?

If using [Av] exposure mode, what setting is selected for [C.Fn I:Exposure → Flash sync. speed in Av mode]?

It's entirely possible that a slower shutter time was forced by the use of the flash, depending on your camera's settings at the time. It's also possible that your tripod is not as stable as you might want (or the surface it is sitting on is not as stable as you might want).

Some flashes also produce pulses of hot air directly in front of the flash head. The sudden change in air pressure directly in front of the flash head can cause the same kind of force acting on the flash as a small gust of wind would.

You didn't bother to specify whether you are using an external flash or not, a camera-mounted flash or remote, and which brand of flash.

You mention "Flash was on ETTL". That counts towards an external flash. Which is too bad since I have a better explanation for an internal flash (voltage drop) but it can be stretched to match external.

Image stabilisation is done by the lens. For that it needs information from the camera and current from the camera. The current is used for suspending and moving the image stabilisation elements in a magnetic field.

Now what happens is that at the moment of firing the flash, something significantly changes for the IS. The communication gets messed up due to the electromagnetic pulse of a rapid discharge or the available voltage/current for working the image stabilisation drops because the flash recharge circuitry starts drawing large current. Additional current is drawn by the lens aperture closing down to its nominal value: that may also cause some mechanical unrest so you might try whether it makes a difference to shoot at maximum aperture.

Also check the shutter speed taken: usually it should just be the flash's and camera's sync speed.

So things to try: maximum aperture (reduces aperture action but also flash power, so it's not a completely isolated test), fresh batteries or use the mains power supply, double-check the lens contacts to be clean (when in doubt, cleaning them with a bit of alcohol on a cotton swab might be an idea) and the lens to be mounted and locked well. Try using external instead of internal flash and vice versa or a different external flash.

You have found a workaround but it would be good to figure out what the exact problem is so that you can recognize it when it arises in somewhat different circumstances.

In-lens image stabilization doesn't require any information from the camera. Gyroscopes within the lens are used to detect camera movement; aperture and focal length might affect the stabilization required but the lens already knows those.
– David RicherbyFeb 11 at 15:12

That depend on the implementation of lens-based IS. Some systems do require camera based communication. Even if no "communication" is needed, electrical current certainly is.
– Michael CFeb 12 at 4:48